Surface-treated steel sheet excellent in corrosion resistance, conductivity, and coating appearance

ABSTRACT

A surface-treated steel sheet includes a steel sheet; a plating layer containing at least one metal selected from zinc and aluminum; a first layer film containing (α) 1 to 2000 mg/m 2  of silica in terms of SiO 2 , (β) a total of 1 to 1000 mg/m 2  of phosphoric acid groups in terms of P, (γ) a total of 0.5 to 800 mg/m 2  of at least one metal selected from Mg, Mn, and Al, and (δ) 0.1 to 50 mg/m 2  of a tetravalent vanadium compound; and a second layer film formed to a thickness of 0.1 to 5 μm on the first layer film and containing a resin (A) having at least one type of functional group selected from OH and COOH groups, and at least one rust-proofing additive (B) selected from (a) a phosphate, (b) Ca ion-exchanged silica, (c) a molybdate, (d) silicon oxide, and (e) at least one organic compound selected from triazoles, thiols, thiadiazoles, thiazoles, and thiurams.

TECHNICAL FIELD

This disclosure relates to a surface-treated steel sheet optimum for usein automobiles, household electric appliances, or building materials.Particularly, this disclosure relates to an environment-conscioussurface-treated steel sheet not containing hexavalent chromium (Cr(VI))which is likely to adversely affect workers, users, or environments ofuse during wastewater treatment in manufacturing or handling ofproducts.

BACKGROUND ART

Steel sheets with surfaces plated with zinc- or aluminum-containingcoatings and further treated with chromate are conventionally widelyused as steel sheets for automobiles, household electric appliances, andbuilding materials. In chromate treatment, a chromate layer is formedusing a treatment solution containing hexavalent chromium (Cr(VI)) as amain component, for improving corrosion resistance (resistance to whiterust and resistance to red rust). However, the chromate treatment useshexavalent chromium (Cr(VI)) which is a pollution control substance, andthus a film subjected to non-polluting treatment not using hexavalentchromium (Cr(VI)) has recently been proposed in view of the influence onenvironments and human bodies. In particular, several methods usingorganic compounds or organic resins have been proposed. Examples of suchmethods are given below.

-   -   (1) Japanese Unexamined Patent Application Publication No.        63-90581 discloses a method using a thermosetting paint        containing an epoxy resin, an amino resin, and tannic acid.    -   (2) Japanese Unexamined Patent Application Publication No.        8-325760 discloses a method utilizing the chelating force of        tannic acid by using a mixed composition containing an aqueous        resin and polyhydric phenolcarboxylic acid.    -   (3) Japanese Examined Patent Application Publication No.        53-27694 discloses a surface treatment method in which a        hydrazine derivative aqueous solution is coated on a surface of        a tinned or galvanized steel sheet.    -   (4) Japanese Unexamined Patent Application Publication Nos.        2002-53980 and 2002-53979 disclose a technique for forming a        phosphoric acid and/or phosphoric acid compound film containing        an oxide as a lower layer, and then forming an organic composite        coating comprising a resin film as an upper layer.

However, these conventional techniques have the following problems:

-   -   Any one of methods (1) to (3) causes insufficient corrosion        resistance due to the fact that the resulting film has no        self-healing effect.    -   The corrosion resistance of a chromate film is exhibited by the        synergetic effect of a barrier effect and a self-healing effect.        The barrier effect is a barrier effect against corrosion factors        (water, oxygen, chlorine, and the like) of a slightly soluble        compound (hydrous oxide) mainly composed of trivalent Cr. The        self-healing effect is the effect of forming a protective film        by hexavalent Cr (Cr(VI)) at a corrosion origin.    -   In chromium-free techniques (1) to (3), the barrier effect can        be imparted to some extent by an organic resin or the like        without using chromium. However, the self-healing effect cannot        be exhibited by hexavalent Cr (Cr(VI)), and thus a high degree        of corrosion resistance cannot be realized.    -   On the other hand, in technique (4), the corrosion resistance is        improved to some extent by adding a specified substance        exhibiting the self-healing effect to the upper layer. However,        the corrosion resistance is not necessarily sufficiently        improved. This is because the film formed at the interface        between the zinc coating and the upper layer, i.e., the lower        layer, does not contain hexavalent Cr (Cr(VI)), thereby failing        to obtain a direct rust-proofing effect due to the self-healing        effect.

Accordingly, it could be advantageous to provide a surface-treated steelsheet exhibiting excellent corrosion resistance, excellent conductivity,and excellent coating appearance even when the film does not contain apollution control substance such as hexavalent chromium (Cr(VI)).

SUMMARY

We provide a surface-treated steel sheet comprising:

-   -   a steel sheet;    -   a plating layer provided on at least one of the surfaces of the        steel sheet, the plating layer containing at least one metal        selected from the group consisting of zinc and aluminum;    -   a first layer film provided on the surface of the plating layer,        the first layer film containing (α) 1 to 2000 mg/m² of silica in        terms of SiO₂, (β) a total of 1 to 1000 mg/m² of phosphoric acid        groups in terms of P, (γ) a total of 0.5 to 800 mg/m² of at        least one metal selected from the group consisting of Mg, Mn,        and Al in terms of a metal element, and (δ) 0.1 to 50 mg/m² of a        tetravalent vanadium compound in terms of V; and    -   a second layer film formed to a thickness of 0.1 to 5 μm on the        first layer film and containing a resin (A) having at least one        type of functional group selected from the group consisting of        OH and COOH groups, and at least one rust-proofing additive (B)        selected from the group consisting of the following        compounds (a) to (e):        -   (a) a phosphate;        -   (b) Ca ion-exchanged silica;        -   (c) a molybdate;        -   (d) silicon oxide; and        -   (e) at least one organic compound selected from the group            consisting of triazoles, thiols, thiadiazoles, thiazoles,            and thiurams.

In the surface-treated steel sheet, the resin (A) is preferably aproduct (X) of reaction of a film-forming organic resin with an activehydrogen-containing substance (D) partially or entirely comprising ahydrazine derivative (C) having active hydrogen.

We also provide a surface-treated steel sheet having excellent corrosionresistance, conductivity, and coating appearance, the steels sheetcomprising a steel sheet having a zinc-based or aluminum-based coating,a composite oxide film formed as a first layer film on a surface of thesteel sheet and containing (α) silica, (β) phosphoric acid and/or aphosphoric acid compound, (γ) at least one metal selected from the groupconsisting of Mg, Mn, and Al (the metal may be contained as a compoundand/or a complex compound), and (δ) a tetravalent vanadium (IV)compound, the coating weights of these components being as follows:

-   -   (α) silica: 1 to 2000 mg/m² in terms of SiO₂;    -   (β) phosphoric acid and/or a phosphoric acid compound: a total        of 1 to 1000 mg/m² in terms of P;    -   (γ) at least one metal selected from the group consisting of Mg,        Mn, and Al: a total of 0.5 to 800 mg/m² in terms of Mg, Mn, and        Al; and    -   (δ) a tetravalent vanadium compound: 0.1 to 50 mg/m² in terms of        V; and an organic film formed as a second layer film having a        thickness of 0.1 to 5 μm on the first layer film and containing        an organic polymeric resin (A) having an OH group and/or a COOH        group, and at least one rust-proofing additive (B) selected from        the group consisting of the compounds (a) to (e) below in a        total of 1 to 100 parts by mass (solid content) relative to 100        parts by mass (solid content) of the resin (A):        -   (a) a phosphate;        -   (b) Ca ion-exchanged silica;        -   (c) a molybdate;        -   (d) silicon oxide; and        -   (e) at least one organic compound selected from the group            consisting of triazoles, thiols, thiadiazoles, thiazoles,            and thiurams.

DETAILED DESCRIPTION

As a result of intensive research, we found that corrosion resistancecan be significantly improved by forming a specified composite oxidefilm containing a tetravalent vanadium compound as a first layer film ona surface of a steel sheet having a coating containing at least onemetal selected from zinc and aluminum, and then forming an organic filmas a second layer film on the first layer film, the organic filmcontaining a specified organic polymeric resin and a specifiedself-healing substance at an appropriate ratio.

Details will be described below.

Usable examples of a steel sheet having a zinc-containing coating andused as a base of a surface-treated steel sheet of the present inventioninclude a galvanized steel sheet, a Zn—Ni alloy plated steel sheet, aZn—Fe alloy plated steel sheet (electroplated steel sheet or alloyinghot-dip galvanized steel sheet), a Zn—Cr alloy plated steel sheet, aZn—Mn alloy plated steel sheet, a Zn—Co alloy plated steel sheet, aZn—Co—Cr alloy plated steel sheet, a Zn—Cr—Ni alloy plated steel sheet,a Zn—Cr—Fe alloy plated steel sheet, a Zn—Al alloy plated steel sheet(for example, a Zn-5% Al alloy plated steel sheet or Zn-55% Al alloyplated steel sheet), a Zn—Mg alloy plated steel sheet, Zn—Al—Mg alloyplated steel sheet, further a zinc or a zinc alloy composite platedsteel sheets prepared by dispersing a metallic oxide, a polymer, or thelike into the plating film of any one of the aforementioned plated steelsheets (for example, Zn—SiO₂ dispersion-plated steel sheets).

Among these plated-steel sheets, a multilayer-plated steel sheet havingat least two plating layers which are the same or different may be used.

As the steel sheet having an aluminum-containing coating and used as thebase of the surface-treated steel sheet, an aluminum-plated steel sheet,an Al—Si alloy plated steel sheet, or the like can be used.

The plated steel sheet may be produced by plating a surface of a steelsheet with Ni at a low coating weight, and then plating the steel sheetwith any one of the above-described plating layers.

As the plating method, any one of practicable methods such aselectrolytic method (electrolysis in an aqueous solution or anon-aqueous solvent), a hot-dipping method, and a vapor phase method.

When the two-layer plating film is formed on the plating film asdescribed below, in order to prevent the occurrence of defects orunevenness in the surface of the plating film, the plating film surfacecan be previously treated by alkali degreasing, solvent degreasing,surface controlling (alkaline surface controlling or acidic surfacecontrolling), or the like according to demand. In order to preventblackening (a type of oxidation phenomenon of a plated surface) in anenvironment in which the surface-treated steel sheet is used, thesurface of the plating film can be previously treated by surface controlwith an acid or alkali aqueous solution containing an iron-group metalion (at least one selected from Ni ion, Co ion, and Fe ion) according todemand. When the electrogalvanized steel sheet is used as the base steelsheet, in order to prevent blackening, an iron-group metal ion (at leastone selected from Ni ion, Co ion, and Fe ion) may be added to anelectroplating bath so that the plating film contains 1 ppm or more ofthe metal. In this case, the upper limit of the content of theiron-group metal contained in the plating film is not particularlylimited.

Next, description will be made of the first layer film (referred to as a“composite oxide film” hereinafter) formed on the surface of the platedsteel sheet of the present invention.

The composite oxide film is completely different from a conventionalalkali silicate treatment film represented by a film compositioncomprising lithium oxide and silicon oxide. Namely, the first layer filmof the present invention is the composite oxide film containing thefollowing components:

-   -   (α) silica;    -   (β) a phosphoric acid group;    -   (γ) at least one metal selected from Mg, Mn, and Al; and    -   (δ) a tetravalent vanadium compound.

By adding the four components, the specific rust-proofing effectdescribed below can be obtained.

As the silica as component (α), colloidal silica is particularlypreferred from the viewpoint of corrosion resistance. In particular,silica having a particle diameter of 14 nm or less, preferably 8 nm orless, is preferred.

Alternatively, a dispersion of fumed silica fine particles in a filmcomposition solution can be used. In this case, the particle diameter ispreferably 12 nm or less, and more preferably 7 nm or less.

The coating weight of component (α) in the film per side is 1 to 2000mg/m² in terms of SiO₂. When the coating weight is less than 1 mg/m² interms of SiO₂, the effect of addition of component (α) cannot besufficiently expected. On the other hand, when the coating weightexceeds 2000 mg/m², problems of adhesion and blackening occur. Thecoating weight is more preferably 5 to 1000 mg/m², and most preferably10 to 200 mg/m².

Next, the phosphoric acid group as component (β) will be described. Ingeneral, the term “acid group” means a residual radical after at leastone hydrogen atom replaceable with a metal is removed from an acidmolecule. In the present invention, the “phosphoric acid group” means aresidual radical after at least one hydrogen atom replaceable with ametal is removed from a phosphoric acid analogue. Such a phosphoric acidanalogue represents a phosphorus-containing acid. Examples of thephosphoric acid analogue include a series of acids produced by variousdegrees of hydration of phosphorus pentoxide, such as condensedphosphoric acids, for example, orthophosphoric acid, metaphosphoricacid, pyrophosphoric acid, tripolyphosphoric acid, and polyphosphoricacid, and phosphorous acids such as phosphorous acid and hypophosphorousacid. More specifically, phosphoric acid and/or a phosphoric acidcompound is used as the phosphoric acid group. Examples of thephosphoric acid and/or phosphoric acid compound include theabove-described phosphoric acid analogues and various salts thereof.These compounds may be used alone or in a mixture of two or more.Examples of salts of orthophosphoric acid include primary phosphates,secondary phosphates, and tertiary phosphates. At least one of the metalsalts and the compounds can be mixed as a film component by adding tothe film composition.

The tetravalent vanadium compound as component (δ) may include avanadium compound with another valency as long as the tetravalentvanadium compound is contained as a main component (50 wt % or more). Ofcourse, the content of the tetravalent vanadium compound as component(δ) is preferably as high as possible, and only the tetravalent vanadiumcompound is more preferably added as component (δ). Preferred examplesof the tetravalent vanadium compound include an oxide, hydroxide,sulfide, sulfate, carbonate, halide, nitride, fluoride, carbide, andcyanide (thiocyanide) of tetravalent vanadium, and salts thereof. Thesecompounds can be used alone or in a mixture of two or more. As thetetravalent vanadium compound, a tetravalent vanadium compound producedby reducing a pentavalent vanadium compound using a reducing agent ispreferably used from the viewpoint of corrosion resistance andresistance to blackening. In this case, the reducing agent used may beeither inorganic or organic, but an organic agent is more preferred.

The coating weight of component (β) in the film per side is 1 to 1000mg/m² in total in terms of P. When the coating weight is less than 1mg/m² in terms of P, the effect of addition of component (β) cannot besufficiently expected. On the other hand, when the coating weightexceeds 1000 mg/m², problems with corrosion resistance and spotweldability occur. The coating weight is more preferably 5 to 500 mg/m²,and most preferably 10 to 100 mg/m².

The form of at least one metal selected from Mg, Mn, and Al and presentas component (γ) in the film is not particularly limited. The metal maybe contained as a compound and/or a complex compound. The metal isusually added to the film as a part of a metal compound. The metal maybe present as an elemental metal, a compound such as an oxide, ahydroxide, a hydrous oxide, a phosphoric acid compound, a coordinationcompound, or the like, or a complex compound. The ionicity andsolubility of these compounds such as a hydroxide, a hydrous oxide, aphosphoric acid compound, a coordination compound, and the like are notparticularly limited. Therefore, the metal component may be a metalcontained as a part of the phosphoric acid compound, or a metalcontained as a part of another metal compound. The film of the presentinvention does not eliminate the coexistence of another metal or metalcompound. However, of course, chromium or a chromium compound isexcluded in view of the pollution prevention purpose of the presentinvention. This is because a chromium-free film is obtained.

In an example of the method for introducing component (γ) in the film, aphosphate, a sulfate, a nitrate, a chloride, or the like of Mg, Mn, orAl may be added to the film composition.

The coating weight of component (γ) in the film per side is 0.5 to 800mg/m² in terms of a total of Mg, Mn, and Al. When the coating weight isless than 0.5 mg/m² in terms of a total of Mg, Mn, and Al, the effect ofaddition of component (γ) cannot be sufficiently expected. On the otherhand, when the coating weight exceeds 800 mg/m², problems of corrosionresistance and film appearance occur. The coating weight is morepreferably 1 to 500 mg/m², and most preferably 5 to 100 mg/m².

In the present invention, the tetravalent vanadium compound as component(δ) may include a vanadium compound with another valency as long as thetetravalent vanadium compound is contained as a main component (50 wt %or more). Of course, the content of the tetravalent vanadium compound ascomponent (δ) is preferably as high as possible, and only thetetravalent vanadium compound is more preferably added as component (δ).Preferred examples of the tetravalent vanadium compound include anoxide, hydroxide, sulfide, sulfate, carbonate, halide, nitride,fluoride, carbide, and cyanide (thiocyanide) of tetravalent vanadium,and salts thereof. These compounds can be used alone or in a mixture oftwo or more. As the tetravalent vanadium compound, a tetravalentvanadium compound produced by reducing a pentavalent vanadium compoundusing a reducing agent is preferably used from the viewpoint ofcorrosion resistance and resistance to blackening. In this case, thereducing agent used may be either inorganic or organic, but an organicagent is more preferred.

When a pentavalent vanadium compound is used as a main component ofcomponent (δ), a uniform film cannot be formed due to the low stabilityof a treatment solution, thereby failing to achieve sufficient corrosionresistance. When a divalent or trivalent vanadium compound is used as amain component, the corrosion resistance is unsatisfactory. On the otherhand, when the tetravalent vanadium compound is used, such a problemdoes not occur. Therefore, the excellent corrosion resistance can beachieved by the synergic effect of components (α) to (γ).

The coating weight of component (δ) in the film per side is 0.1 to 50mg/m² in terms of V. When the coating weight is less than 0.1 mg/m² interms of V, the effect of addition of component (δ) cannot besufficiently expected. On the other hand, when the coating weightexceeds 50 mg/m², problems of coloring and blackening occur. The coatingweight is more preferably 0.5 to 30 mg/m², and most preferably 1 to 10mg/m².

When the first film (composite oxide film) containing the abovecomponents is formed on the plated steel sheet, extremely excellentcorrosion resistance can be achieved. Although not necessarily known,the possible reason for this lies in the following mechanism:

-   -   First, with respect to the function as a barrier film, the        compact, slightly soluble composite oxide film blocks a        corrosion factor to exhibit a high degree of barrier effect.        This is possibly due to the functions: (i) Silica forms a stable        compact barrier film together with the phosphoric acid or        phosphoric acid compound and the metal as the component        (γ). (ii) The silicate acid ions in silica promote the formation        of basic zinc chloride in a corrosive environment to improve the        barrier property. (iii) A slightly soluble salt is formed by        tetravalent vanadium ions VO₂ ⁺ and complex ions thereof (for        example, [VO(SO₄)₂]²⁻) of the tetravalent vanadium compound        added and phosphoric acid ions in the film, thereby improving        the barrier property. (iv) A uniform film can be formed because        the tetravalent vanadium compound has excellent stability of the        treatment solution, unlike a pentavalent vanadium compound. In        particular, a compact and slightly soluble film containing the        metal as component (γ) and the vanadium compound included        through bonds to the phosphoric acid ions and silica may be        formed, and functions (i) to (iv) discribed above may be        organically combined to achieve a high degree of barrier effect.

The composite oxide film further has an excellent self-healing effect inaddition to the above-described high degree of barrier effect. This ispossibly due to the functions: (I) When a defect occurs in the film, OHions are produced by cathode reaction to alkalinize the interface, andthus component (γ) precipitates as a metal hydroxide, which is a compactand slightly soluble product, and seals the defect, thereby preventingcorrosion. (II) As described above, the phosphoric acid or phosphoricacid compound contributes to the compactness of the composite oxidefilm, and zinc ions dissolved in a film defect due to anodic reaction,which is corrosion reaction, are captured by the phosphoric acidcomponent to form a precipitate product as a slightly soluble zincphosphate compound. (III) The tetravalent vanadium compound is reducedby its own oxidizing function to form an oxide or hydroxide film on thesurface of the plating layer, the oxide or hydroxide film exhibiting aself-healing function. With respect to the self-healing function,particularly, a film containing the metal as the component (γ) and thevanadium compound, which are included through bonds to the phosphoricacid ions and silica, is formed, and the functions (I) to (III) areorganically combined to achieve a high degree of self-healing effect.

The extremely excellent corrosion resistance is realized by theabove-described high degrees of barrier effect and self-healing effect.

Next, the second layer film (referred to as the “organic film”hereinafter) formed on the composite oxide film (first layer film) willbe described.

The organic film formed on the first layer film contains an organicpolymeric resin (A) (referred to as a “resin (A)” hereinafter) having atleast one functional group selected from the group consisting of OH andCOOH groups, and at least one rust-proofing additive (B) selected fromthe group consisting of the following self-healing substances (a) to(e):

-   -   (a) a phosphate;    -   (b) Ca ion-exchanged silica;    -   (c) a molybdate;    -   (d) silicon oxide; and    -   (e) at least one organic compound selected from triazoles,        thiols, thiadiazoles, thiazoles, and thiurams.

The rust-proofing additive may contain at least one substance selectedfrom the group consisting of the substances (a) to (e) as a maincomponent.

As a base resin of the organic film, the organic polymeric resin (A)having OH and/or COOH is used. The base resin means a raw material resinused for forming the organic film containing the rust-proofing additive(B).

Preferred examples of the organic polymeric resin (A) include epoxyresins, polyhydroxy polyether resins, acrylic copolymer resins,ethylene-acrylic acid copolymer resins, alkyd resins, phenol resins, andpolyurethane resins. However, even if a monomer used as a raw materialdoes not contain OH and/or COOH, an OH group and/or a COOH group can beintroduced in the resin (A) by oxidizing or carbonating the resin.Examples of such a raw material resin include polybutadiene resins,polyamine resins, and polyphenylene resins. The resin (A) can also beproduced by copolymerization with a compound having an OH group and/or aCOOH group or modification with a compound having an OH group and/or aCOOH group. These resins may be used in a mixture or as an additionpolymer of two or more.

Examples of such a resin include modified epoxy resins, acryliccopolymer resins copolymerized with an epoxy-containing monomer,epoxy-containing polybutadiene resins, epoxy-containing polyurethaneresins, and adducts or condensates of these resins.

Epoxy Resin

Usable examples of epoxy resins include glycidyl-etherified epoxy resinsproduced from bisphenol A, bisphenol F, or novolak, glycidyl-etherifiedepoxy resins produced by adding propylene oxide, ethylene oxide, orpolyalkylene glycol to bisphenol A, aliphatic epoxy resins, alicyclicepoxy resins, and polyether epoxy resins.

Particularly, when low-temperature curing is required, the epoxy resinpreferably has a number-average molecular weight of 1500 or more.

The modified epoxy resins can be produced by reacting the epoxy groupsor hydroxyl groups of the above-mentioned epoxy resins with any one ofvarious modifiers. Examples of the modified epoxy resins includeepoxyester resins produced by reaction with carboxyl groups indrying-oil fatty acids, epoxyacrylate resins produced by modificationwith acrylic acid or methacrylic acid, urethane-modified epoxy resinsproduced by reaction of epoxy resins with isocyanate compounds, andamine-added urethane-modified epoxy resins produced by adding alkanolamine to urethane-modified epoxy resins produced by reaction withisocyanate compounds.

Examples of the acrylic copolymer resins copolymerized with anepoxy-containing monomer include resins synthesized by solutionpolymerization, emulsion polymerization, or suspension polymerization ofan epoxy-containing unsaturated monomer, and a polymerizable unsaturatedmonomer component essentially including an acrylic acid ester ormethacrylic acid ester.

Examples of the polymerizable unsaturated monomer component include C1to C24 alkyl esters of acrylic acid or methacrylic acid, such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-, iso- ortert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate; acrylicacid, methacrylic acid, styrene, vinyl toluene, acrylamide,acrylonitrile, N-methylol (meth)acrylamide, C1 to C4 alkyl ethers ofN-methylol (meth)acrylamide; and N,N-diethylaminoethyl methacrylate.

Examples of the epoxy-containing unsaturated monomer include glycidylmethacrylate, glycidyl acrylate, and 3,4-epoxycyclohexylmethyl(meth)acrylate. The epoxy-containing unsaturated monomer is notparticularly limited as long as is contains an epoxy group and apolymerizable unsaturated group.

The acrylic copolymer resin copolymerized with the epoxy-containingmonomer may be modified with a polyester resin, an epoxy resin, a phenolresin, or the like.

In particular, the epoxy resin is preferably a product of reactionbetween bisphenol A and epihalohydrin because of excellent corrosionresistance, the product being a resin having a chemical structurerepresented by formula (1).

A method for producing the bisphenol A epoxy resin is widely used in theindustry. In the above chemical structure, q is 0 to 50, preferably 1 to40, and more preferably 2 to 20.

The resin (A) may be any one of an organic solvent-soluble type, anorganic solvent-dispersible type, a water-soluble type, and awater-dispersible type.

The polyhydroxy polyether resin is a polymer produced bypolycondensation of a mononuclear or dinuclear dihydric phenol or amixture of mononuclear and dinuclear dihydric phenols with substantiallyan equal mole of epihalohydrin in the presence of an alkali catalyst.Typical examples of the mononuclear dihydric phenol include resorcin,hydroquinone, and catechol. Typical examples of the binuclear phenolinclude bisphenol A.

Phenol Resin

Phenol resins are thermosetting resins produced by reaction of phenolswith formaldehyde, and conventional phenol resins can be directly used.For example, cresol resins and xylenol resins can also be used.

Urethane Resin

Examples of urethane resins include oil-modified polyurethane resins,alkyd polyurethane resins, polyester urethane resins, polyether urethaneresins, and polycarbonate polyurethane resins.

Alkyd Resin

Examples of alkyd resins include oil-modified alkyd resins,rosin-modified alkyd resins, phenol-modified alkyd resins, styrene alkydresins, silicon-modified alkyd resins, acryl-modified alkyd resins,oil-free alkyd resins, and high-molecular-weight oil-free alkyd resins.

Acrylic Resin

Examples of acrylic resins include polyacrylic acid and copolymersthereof, polyacrylic acid esters and copolymers thereof, polymethacrylicacid esters and copolymers thereof, urethane-acrylic acid copolymers (orurethane-modified acrylic resins), and styrene-acrylic acid copolymers.These resins may be further modified with another alkyd resin, epoxyresin or phenol resin.

Polyolefin Resin (Ethylene Resin)

Examples of polyolefin resins include ethylene resins such asethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers,and carboxyl-modified polyolefin resins; ethylene-unsaturated carboxylicacid copolymers; and ethylene ionomers. These resins may be furthermodified with another alkyd resin, epoxy resin or phenol resin.

Acrylsilicone Resin

Examples of acrylsilicone resins include resins each containing anacrylic copolymer as a base resin, which has a hydrolyzable alkoxysilylgroup in its side chain or terminal, and a curing agent added thereto.When such an acrylsilicone resin is used, excellent weather resistancecan be expected.

Fluororesin

Examples of fluororesins include fluoroolefin copolymers, for example, acopolymer produced by copolymerization of a fluorine monomer(fluoroolefin) with another monomer such as an alkyl vinyl ether, acycloalkyl vinyl ether, a carboxylic acid-modified vinyl ester, ahydroxyalkyl allyl ether, or tetrafluoropropyl vinyl ether.

When such a fluororesin is used, excellent weather resistance andexcellent hydrophobicity can be expected.

Among the above-described resins, thermosetting resins are preferred.Particularly, an epoxy resin and modified epoxy resin having anexcellent block property against a corrosive factor such as oxygen areoptimum. Even when the coating weight of the film is decreased forrealizing high degrees of conductivity and spot weldability, the epoxyresin and modified epoxy resin are particularly advantageous because thecorrosion resistance and film appearance can be maintained.

To improve the corrosion resistance of the organic film, a thermosettingresin and a curing agent are preferably mixed. In this case, an aminoresin such as an urea resin (e.g.butylated urea resin or the like), amelamine resin (e.g.butylated melamine resin), a butylated urea-melamineresin, a benzoguanamine resin, or the like, block isocyanate, anoxazoline compound, a phenol resin, or the like can be added as thecuring agent.

In order to decrease the drying temperature of the resin, awater-dispersible resin comprising core-shell structure each usingresins having different glass transition temperatures for the core andthe shell, respectively, can be used.

Alternatively, a self-crosslinkable, water-dispersible resin can beused. For example, when an alkoxysilane group is introduced to the resinparticles, during heat-drying of the resin, crosslinking can be producedbetween the particles by the formation of a silanol group due tohydrolysis of the alkoxysilane and dehydration condensation reaction ofthe silanol group between the resin particles.

As the resin used for the organic film, an organic complex silicateproduced by combining an organic resin and silica with a silane couplingagent is also preferred.

The organic polymeric resin (A) is preferably a product (X) of reactionof a film-forming organic resin with an active hydrogen-containingmaterial (D) entirely or partially comprising a hydrazine derivative (C)having active hydrogen. The active hydrogen-containing material (D) maybe a mixture or a compound. Namely, the active hydrogen-containingmaterial (D) entirely or partially comprises the hydrazine derivative(C) having active hydrogen. In the present invention, the resin (A) (orthe organic polymeric resin (A)) is more preferably the reaction product(X) produced by modifying the film-forming organic resin with the activehydrogen-containing material (D), the product (X) corresponding to amodified resin having an OH group and/or COOH group.

In order to more clearly define the active hydrogen-containing material(D), each of the constituent units will be described in further detailbelow.

As the film-forming organic resin (A), a resin containing an epoxy groupis particularly preferred from the viewpoint of reactivity and corrosionresistance. The epoxy group-containing resin (E) is not particulalylimited as long as the resin (E) can react with the activehydrogen-containing material (D) entirely or partially comprising thehydrazine derivative (C) having active hydrogen, thus the activehydrogen-containing material (D) can be bonded to the film-formingorganic resin by the reactions such as addition or condensation, and afilm can be properly formed.

It is desired that the hydrazine derivative (C) is introduced to themolecule of the film-forming organic resin (A). Therefore, at least apart (preferably the whole) of the active hydrogen-containing material(D) is composed of the hydrazine derivative (C) having active hydrogen.In the present invention, the active hydrogen can be determined by thepresence of reactivity to the resin. For example, hydrogen reactive toan epoxy group can be determined to be active hydrogen.

When the film-forming organic resin (A) is the epoxy-containing resin(E), for example, the active hydrogen-containing material (D) reactiveto the epoxy group has the following component:

-   -   a hydrazine derivative having active hydrogen;    -   a primary or secondary amine compound having active hydrogen;    -   ammonia or an organic acid such as a carboxylic acid or the        like;    -   hydrogen halide such as hydrogen chloride or the like; or    -   an alcohol or thiol.    -   A quaternary salt forming agent comprising a mixture of an acid        and a hydrazine derivative not having active hydrogen or a        tertiary amine

At least one of these compounds may be used. In this case, at least apart (preferably the whole) of the active hydrogen-containing material(D) must be the hydrazine derivative.

Examples of the hydrazine derivative (C) having active hydrogen includethe following:

-   -   (1) hydrazide compounds such as carbohydrazide, propionic acid        hydrazide, salicylic acid hydrazide, adipic acid dihydrazide,        sebacic acid dihydrazide, dodecanoic acid dihydrazide,        isophthalic acid dihydrazide, thiocarbohydrazide,        4,4′-oxybisbenzenesulfonyl hydrazide, benzophenone hydrazide,        and aminopolyacrylamide;    -   (2) pyrazole compounds such as pyrazole, 3,5-dimethylpyrazole,        3-methyl-5-pyrazolone, and 3-amino-5-methylpyrazole;    -   (3) triazole compounds such as 1,2,4-triazole,        3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole,        3-mercapto-1,2,4-triazole, 5-amino-3-mercapto-1,2,4-triazole,        2,3-dihydro-3-oxo-1,2,4-triazole, 1H-benzotriazole,        1-hydroxybenzotriazole (monohydrate),        6-methyl-8-hydroxytriazolopyridazine,        6-phenyl-8-hydroxytriazolopyridazine, and        5-hydroxy-7-methyl-1,3,8-triazaindolizine;    -   (4) tetrazole compounds such as 5-phenyl-1,2,3,4-tetrazole and        5-mercapto-1-phenyl-1,2,3,4-tetrazole;    -   (5) thiadiazole compounds such as        5-amino-2-mercapto-1,3,4-thiadiazole,        2,5-dimercapto-1,3,4-thiaziazole; and    -   (6) pyridazine compounds such as maleic acid hydrazide,        6-methyl-3-pyridazone, 4,5-dichloro-3-pyridazone,        4,5-dibromo-3-pyridazone, and 6-methyl-4,5-dihydro-3-pyridazone.

Among these derivatives, pyrazole compounds and triazole compounds, thathave five-member rings, are particularly preferred.

These hydrazine derivatives can be used alone or in a mixture of two ormore.

Typical examples of the amine compound having active hydrogen, which canbe used as a part of the active hydrogen-containing material (D),include the following compounds:

-   -   (1) compounds modified to aldimine, ketimine, oxazoline, or        imidazoline by reaction of a primary amino group of an amine        compound having one secondary amino group and at least one        primary amino group, such as diethylenetriamine,        hydroxyethylaminoethylamine, ethylaminoethylamine, or        methylaminopropylamine, with a keto compound such as a ketone,        an aldehyde, or a carboxylic acid at a temperature of, for        example, about 100° C. to 230° C.;    -   (2) secondary monoamines such as diethylamine, dibutylamine,        diethanolamine, di-n- or -iso-propanolamine,        N-methylethanolamine, and N-ethylethanolamine;    -   (3) secondary amine-containing compounds produced by addition        reaction, e.g., Michael addition reaction, of monoalkanolamine        such as monoethanolamine with dialkyl (meth)acrylamide; and    -   (4) compounds produced by modifying a primary amino group of an        alkanolamine such as monoethanolamine, neopentanolamine,        2-aminopropanol, 3-aminopropanol, or        2-hydroxy-2′-(aminopropoxy)ethyl ether to ketimine.

Since a hydrazine derivative not containing active hydrogen or atertiary amine is unreactive to an epoxy group, the quaternary soltforming agent used as a part of the active hydrogen-containing material(D) comprises a mixture of the hydrazine derivative or tertiary mine andan acid in order enable reaction with an epoxy group. According todemand, the quaternary solt forming agent reacts with an epoxy group inthe presence of water to form an epoxy-containing resin and a quaternarysalt.

As the acid used for forming the quaternary solt forming agent, anorganic acid such as acetic acid or lactic acid, an inorganic acid suchas hydrochloric acid can be used. As the hydrazine derivative notcontaining active hydrogen and used for forming the quaternary soltforming agent, for example, 3,6-dichloropyridazine or the like can beused. Examples of the tertiary amine include N,N-dimethylethanolamine,triethylamine, trimethylamine, triisopropylamine, andmethyldiethanolamine.

The reaction product (X) of reaction between the film forming organicresin (A) and the active hydrogen-containing material (D) includingcompounds partially or entirely comprising the activehydrogen-containing hydrazine derivative (C) is preferably produced byreaction of the film-forming organic resin (A) and the activehydrogen-containing material (D) at 10° C. to 300° C., preferably 50° C.to 150° C., for about 1 to 8 hours.

The reaction may be performed in the presence of a solvent, and the typeof the solvent used is not particularly limited. Examples of the solventinclude ketones such as acetone, methyl ethyl ketone, methyl isobutylketone, dibutyl ketone, and cyclohexanone; alcohols and ethers such asethanol, butanol, 2-ethylhexyl alcohol, benzyl alcohol, ethylene glycol,ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether,ethylene glycol monohexyl ether, propylene glycol, propylene glycolmonomethyl ether, diethylene glycol, diethylene glycol monoethyl ether,and diethylene glycol monobutyl ether; esters such as ethyl acetate,butyl acetate, and ethylene glycol monobutyl ether acetate; and aromatichydrocarbons such as toluene and xylene. These solvents can be usedalone or combination or two or more. Among these solvents, the ketone orether solvents are particularly preferred from the viewpoint ofcompatibility with an epoxy resin and film-forming property.

The compounding ratio of the active hydrogen-containing material (D)partially or entirely comprising the active hydrogen-containinghydrazine derivative (C) to the film-forming organic resin (A) ispreferably 0.5 to 20 parts by weight, more preferably 1.0 to 10 parts byweight, relatively to 100 parts by weight of the film-forming organicresin (A).

When the film-forming organic resin (A) is the epoxy-containing resin(E), the compounding ratio of the active hydrogen-containing material(D) to the epoxy-containing resin (E) is properly determined so that theratio [number of active hydrogen atoms/number of epoxy groups] of thenumber of active hydrogen atoms in the active hydrogen-containingmaterial (D) to the number of the epoxy groups in the epoxy-containingresin (E) is 0.01 to 10, more preferably 0.1 to 8, and most preferably0.2 to 4, from the viewpoint of corrosion resistance.

The ratio of the active hydrogen-containing hydrazine derivative (C) inthe active hydrogen-containing material (D) is preferably 10 mol % to100 mol %, more preferably 30 mol % to 100 mol %, and most preferably 40mol % to 100 mol %. When the ratio of the active hydrogen-containinghydrazine derivative (C) is 10 mol % or more, the sufficientrust-proofing function can be imparted to the organic film, therebyimproving the rust-proofing effect as compared with a simple mixture ofa film-forming organic resin and a hydrazine derivative.

To form the compact barrier film, preferably, the curing agent is mixedin the resin composition, and organic film is heat-cured.

Preferred examples of a curing method for forming a film of the resincomposition include a curing method (1) utilizing urethanizationreaction between isocyanate and hydroxyl groups of the resin (A), and acuring method (2) utilizing etherification reaction between analkyl-etherified amino resin and hydroxyl groups of the resin (A), inwhich the alkyl-etherified amino resin is produced by partially orentirely reacting a methylol compound, which is produced by reaction ofat least one compound selected from melamine, urea, and benzoguanaminewith formaldehyde, with a monohydric alcohol having 1 to 5 carbon atoms.In particular, the urethanization reaction of an isocyanate and hydroxylgroups of the resin (A) is preferably used as main reaction.

The polyisocyanate compound used in the curing method (1) is analiphatic, alicyclic (including heterocyclic) or aromatic isocyanatecompound containing at least two isocyanate groups in its molecule, or acompound produced by partially reacting the isocyanate compound with apolyhydric alcohol. Examples of such a polyisocyanate compound includethe following compounds:

-   -   (1) m- or p-phenylene diisocyanate, 2,4- or 2,6-tolylene        diisocyanate, o- or p-xylylene diisocyanate, hexamethylene        diisocyanate, dimmer acid diisocyanate, and isophorone        diisocyanate; and    -   (2) products of reaction between one or at least two of        compounds (1) with a polyhydric alcohol (a dihydric alcohol such        as ethylene glycol or propylene glycol; trihydric alcohol such        as glycerine or trimethylolpropane; tetrahydric alcohol such as        pentaerythritol; or hexahydric alcohol such as sorbitol or        dipentaerythritol), the products each containing at least two        isocyanate groups per molecule.

These polyisocyanate compounds can be used alone or in a mixture of twoor more.

Examples of a compound which can be used as a protective agent (blockingagent) for the polyisocyanate compounds include the following:

-   -   (1) aliphatic monoalcohols such as methanol, ethanol, propanol,        butanol, and octyl alcohol;    -   (2) monoethers of ethylene glycol and/or diethylene glycol, for        example, methyl, ethyl, propyl (n- or iso), and butyl (n-, iso,        or sec) monoethers; and    -   (3) aromatic alcohols such as phenol and cresol; and    -   (4) oximes such as acetoxime and methyl ethyl ketone oxime. At        least one of these compounds is reacted with the polyisocyanate        compound to produce a polyisocyanate compound stably protected        at least at room temperature.

The polyisocyanate compound (F) is properly mixed as the curing agentwith the film-forming organic resin (A) at a ratio (A)/(F) of 95/5 to55/45 (weight ratio of involatile content), preferably (A)/(F) of 90/10to 65/35. The polyisocyanate compound has water absorption, and thus acompounding ratio (A)/(F) of 55/45 or less is preferred for securing theadhesion of the organic film. When over coating is performed on theorganic film, the unreacted polyisocyanate compound does not move to thecoating to improve the curing and adhesion of the coating. From thisviewpoint, the polyisocyanate compound (F) is preferably mixed at aratio (A)/(F) or 55/45 or less.

Although the film-forming organic resin (A) is sufficiently cross-linkedby adding the cross-linking agent (curing agent), a known acceleratingcatalyst is preferably used for increasing low-temperature crosslinking.Examples of the accelerating catalyst include N-ethylmorpholine,dibutyltin dilaurate, cobalt naphthenate, stannous chloride, zincnaphthenate, and bismuth nitrate.

For example, when an epoxy-containing organic resin is used as thefilm-forming organic resin (A), a known acryl, alkyd or polyester resincan be mixed with the epoxy-containing organic resin in order to improvesome physical properties such as adhesion and the like.

Next, the rust-proofing additive (B) exhibiting the self-healingproperty will be described.

The types of the phosphate used as component (a) includes all types ofsalts including simple salts and double salts. The metal cationconstituting the salt is not limited, and metal cation of any of zincphosphate, magnesium phosphate, calcium phosphate, aluminum phosphate,and the like can be used. Also, the skeleton and the degree ofcondensation of the phosphoric acid ions are not limited, and any one ofa normal salt, a dihydrogen salt, a monohydrogen salt, and a phosphitemay be used. Examples of a normal salt include orthophosphates and allcondensed phosphates such as polyphosphates.

Furthermore, when a calcium compound is added together with thephosphate as component (a), the corrosion resistance can be furtherimproved. The calcium compound may be any one of calcium oxide, calciumhydroxide, and a calcium salt. These calcium compounds may be used aloneor combination of two or more.

Examples of the calcium compound include, without limitation to, normalsalts each containing only calcium as a cation, such as calciumsilicate, calcium carbonate, and calcium phosphate; and double saltseach containing calcium and a cation other than calcium, such ascalcium-zinc phosphate and calcium-magnesium phosphate.

The Ca ion-exchanged silica used as component (b) comprises poroussilica gel powder containing calcium ions fixed to the surfaces thereof,and it releases the Ca ions in a corrosive environment to form aprecipitate film.

Any desired Ca ion-exchange silica can be used. The average particlediameter of the silica is 6 μm or less, and preferably 4 μm or less. Forexample, the silica having an average particle diameter of 2 to 4 μm canbe used. The Ca ion-exchanged silica having an average particle diameterof 6 μm or less improves the corrosion resistance and the dispersionstability in the coating composition.

The Ca concentration in the Ca ion-exchanged silica is preferably 1 wt %or more, and more preferably 2 wt % to 8 wt %. With a Ca concentrationof 1 wt %, the rust-proofing effect can be sufficiently obtained by Carelease. The surface area, pH, and oil absorption of the Caion-exchanged silica are not particularly limited.

Usable examples of the Ca ion-exchanged silica include SHIELDEX C303(average particle diameter: 2.5 to 3.5 μm, Ca concentration: 3 wt %),SHIELDEX AC3 (average particle diameter: 2.3 to 3.1 μm, Caconcentration: 6 wt %), and SHIELDEX AC5 (average particle diameter: 3.8to 5.2 μm, Ca concentration: 6 wt %) (trade names) produced by W. R.Grace & Co.; SHIELDEX (average particle diameter: 3 μm, Caconcentration: 6 to 8 wt %) and SHIELDEX SY710 (average particlediameter: 2.2 to 2.5 μm, Ca concentration: 6.6 to 7.5 wt %) (tradenames) produced by Fuji Silysia Chemical Ltd.

The skeleton and the degree of condensation of the molybdate used ascomponent (c) are not limited. Examples of the molybdate includeorthomolybdates, paramolybdates, and metamolybdates. Types of themolybdate include all salts such as normal salts and double salts.Examples of double salts include phosphate molybdates.

The silicon oxide used as component (d) may be either colloidal silicaor fumed silica. When an aqueous film-forming resin is used as the base,examples of the colloidal silica include Snowtex O, Snowtex N, Snowtex20, Snowtex 30, Snowtex 40, Snowtex C, and Snowtex S (trade names)produced by Nissan Chemical Industries Ltd.; Cataloid S, CataloidSI-350, Cataloid SI-40, Cataloid SA, and Cataloid SN (trade names)produced by Catalyst & Chemicals Co., Ltd.; and Aderite AT-20˜50,Aderite AT-20N, Aderite AT-300, Aderite AT-330S, and Aderite AT20Q(trade names) produced by Asahi Denka Co. Ltd.

When a solvent-type film-forming resin is used as the base, examples ofthe colloidal silica include Organosilica Sol MA-ST-M, Organosilica SolIPA-ST, Organosilica Sol EG-ST, Organosilica Sol E-ST-ZL, OrganosilicaSol NPC-ST, Organosilica Sol DMAC-ST, Organosilica Sol DMAC-ST-ZL,Organosilica Sol XBA-ST, and Organosilica Sol MIBK-ST (trade names)produced by Nissan Chemical Industries Ltd.; and OSCAL-1132, OSCAL-1232,OSCAL-1332, OSCAL-1432, OSCAL-1532, OSCAL-1632, and OSCAL-1722 (tradenames) produced by Catalyst & Chemicals Co., Ltd.

In particular, organic solvent dispersed silica sol has excellentdispersibility, and also has excellent corrosion resistance incomparison to fumed silica.

Examples of the fumed silica include AEROSIL R971, AEROSIL R812, AEROSILR811, AEROSIL R974, AEROSIL R202, AEROSIL R805, AEROSIL 130, AEROSIL200, AEROSIL 300, and AEROSIL 300CF (trade names) produced by NihonAerosil Co., Ltd.

Fine-particle silica contributes to the formation of a compact, stablecorrosion product of zinc in a corrosive environment, and the corrosionproduct compactly formed on a plated surface can possibly suppressacceleration of corrosion.

From the viewpoint of corrosion resistance, the particle diameter of thefine-particle silica is preferably 5 to 50 nm, more preferably 5 to 20nm, and most preferably 5 to 15 nm.

Examples of the organic compound used as component (e) include triazolessuch as 1,2,4-triazole, 3-amino-1,2,4-triazole,3-mercapto-1,2,4-triazole, 5-amino-3-mercapto-1,2,4-triazole, and1H-benzotriazole; thiols such as 1,3,5-triazine-2,4,6-trithiol and2-mercaptobenzimidazole; thiadiazoles such as5-amino-2-mercapto-1,3,4-thiadiazole and2,5-dimercapto-1,3,4-thiadiazole; thiazoles such as2-N,N-diethylthiobenzothiazole and 2-mercaptobenzothiazole; and thiuramssuch as tetraethylthiuram disulfide.

The total amount of the rust-proofing additive (total amount of at leastone self-healing substance selected from components (a) to (e)) mixed inthe organic film is preferably 1 to 100 parts by weight, more preferably5 to 80 parts by weight, and most preferably 10 to 50 parts by weight interms of solid content relative to 100 parts by weight of the resin(organic polymeric resin (A)). The solid content is defined as a solidat the time of mixing. When the compounding amount of the rust-proofingadditive (B) is 1 part by weight or more, the corrosion resistance isimproved. However, a compounding amount of 100 parts by weight or lessis economical.

The dry thickness of the organic film must be 0.1 μm to 5 μm, preferably0.3 μm to 3 μm, and more preferably 0.5 μm to 2 μm. When the thicknessof the organic film is less than 0.1 μm, the corrosion resistance isunsatisfactory, while when the thickness exceeds 5 μm, the conductivitydegrades.

The above-described organic film formed as the second layer filmpossibly has the following rust-proofing mechanism:

The organic polymeric resin (A) (preferably a thermosetting resin andmore preferably an epoxy resin and/or a modified epoxy resin) having anOH group and/or a COOH group forms a compact barrier film by reactionwith the cross-liking agent. The barrier film has the excellent abilityto suppress permeation of a corrosion factor such as oxygen, and the OHgroup and/or COOH group in the molecule has a strong bonding force withthe basis material, thereby possibly achieving excellent corrosionresistance (barrier function).

An appropriate amount of the rust-proofing additive (B) (self-healingsubstance) is mixed in the organic film comprising the specified organicpolymeric resin. As a result, particularly, the excellent rust-proofingability (self-healing effect) can be obtained. The possiblerust-proofing mechanism realized by mixing the components (a) to (e) inthe specified organic film is as follows:

-   -   Component (a) is dissociated into phosphoric acid ions by        hydrolysis in a corrosive environment and forms a protective        film due to complex forming reaction with the eluted metal.

When cation such as Na ions enters the film in a corrosive environment,the Ca ions on the surfaces of the silica used as component (b) arereleased by an ion exchange function. Furthermore, when OH ions areproduced by cathode reaction in a corrosive environment to increase thepH near the plating interface, the Ca ions released from the Caion-exchanged silica precipitate as Ca(OH)₂ near the plating interfaceto seal defects as a compact, slightly soluble product, therebypreventing corrosion reaction. The eluted zinc ions are exchanged withthe Ca ions and fixed to the silica surfaces.

Component (c) exhibits the self-healing effect due to a passivatingeffect. Namely, component (c) forms a compact oxide film on the surfaceof the plating film together with dissolved oxygen in a corrosiveenvironment, and the oxide film seals the corrosion origin to suppresscorrosion reaction.

Component (d) contributes to the formation of a compact and stablecorrosion product of zinc in a corrosive environment, and the corrosionproduct compactly formed on the surface suppresses acceleration ofcorrosion.

Furthermore, component (e) exhibits the self-healing property due to anadsorption effect. Namely, zinc and aluminum eluted by corrosion areadsorbed on a nitrogen- or sulfur-containing polar group in component(e) to form an inert film, and the inert film seals the corrosion originto suppress corrosion reaction.

Even when components (a) to (e) are mixed in a general organic film, therust-proofing effect can be obtained to some extent. However, as in thepresent invention, when components (a) to (e) as the self-healingsubstances are mixed in the organic film having excellent barrierproperty and comprising the specified organic polymeric resin, botheffects (barrier effect and self-healing effect) may be combined toexhibit the excellent rust-proofing effect.

Furthermore, when a calcium compound is added together with component(a), the calcium compound is eluted in preference to the plating metalin a corrosive environment, and thus causes complex formation reactionwith phosphoric acid ions to form a compact, slightly soluble protectivefilm without using elusion of the plating metal as a trigger, therebysuppressing corrosion reaction.

When at least two of components (a) to (e) is added, the corrosionsuppressing functions of the components are combined to exhibit the moreexcellent corrosion resistance.

In addition to the rust-proofing additive, the organic film may contain,as a corrosion inhibitor, at least one of other oxide fine particles(for example, aluminum oxide, zirconium oxide, titanium oxide, ceriumoxide, antimony oxide, and the like); phosphomolybdates (for example,aluminum phosphomolybdate, and the like); organic phosphoric acid andits salts (for example, phytic acid, phytates, phosphonic acid,phosphonates, and metal salts, alkali metal salts, and alkali earthmetal salts thereof), organic inhibitors (for example, hydrazinederivatives, thiol compounds, dithiocarbamates, and the like).

Furthermore, a solid lubricant can be mixed in the organic film in orderto improve the workability of the film according to demand.

Examples of the solid lubricant include the following. These compoundsmay be used alone or in combination of two or more.

-   -   (1) Polyolefin wax and paraffin wax: for example, polyethylene        wax, synthetic paraffin, natural paraffin, micro wax, and        chlorinated hydrocarbons.    -   (2) Fluororesin fine particles: for example, polyfluoroethylene        resin (polytetrafluoroethylene resin), polyvinyl fluoride resin,        and polyvinylidene fluoride resin.

Other examples include fatty acid amide compounds (for example, stearicamide, palmitic amide, methylenebisstearamide, ethylenebisstearamide,oleic amide, erucic amide, alkylene bis-fatty acid amides, and thelike); metal soaps (for example, calcium stearate, lead stearate,calcium laurate, calcium palmitate, and the like); metal sulfides (forexample, molybdenum disulfide, tungsten disulfide, and the like);graphite; graphite fluoride; boron nitride; polyalkylene glycol; alkalimetal sulfates; and the like.

Among these solid lubricants, polyethylene wax, fluororesin fineparticles (particularly, polytetrafluoroethylene resin fine particles)are particularly preferred.

Examples of the polyethylene wax include Ceridust 9615A, Ceridust 3715,Ceridust 3620, and Ceridust 3910 (trade names) produced by Hoechst JapanLtd.; Sanwax 131-P and Sanwax 161-P (trade names) produced by SanyoChemical Industries, Ltd; and Chemipearl W-100, Chemipearl W-200,Chemipearl W-500, Chemipearl W-800, and Chemipearl W-950 (trade names)produced by Mitsui Petrochemical Industries, Ltd.

As the fluororesin fine particles, tetrafluoroethylene fine particlesare most preferred. Preferred examples of the fine particles includeLubron L-2 and Lubron L-5 (trade names) produced by Daikin Industries,Ltd.; MP1100 and MP1200 (trade names) produced by Mitsui-Dupont Co.,Ltd.; Fluon Dispersion AD1, Fluon Dispersion AD2, Fluon L141J, FluonL150J, and Fluon L155J (trade names) produced by Asahi ICIFluoropolymers Co., Ltd.

In particular, the excellent lubricating effect can be expected bycombination of the polyolefin wax and tetrafluoroethylene fineparticles.

The amount of the solid lubricant mixed in the organic film is 1 to 80parts by weight, and preferably 3 to 40 parts by weight, relative to 100parts by weight of the resin (organic polymeric resin (A)). When theamount of the solid lubricant mixed is 1 part by weigh or more, thesufficient lubricating effect can be obtained, while when the amount ofthe solid lubricant mixed is 80 parts by weight or less, thepaintability is desirably improved.

According to demand, the organic film may further contain as an additiveat least one of an organic coloring pigment (for example, a condensedpolycyclic organic pigment, a phthalocyanine organic pigment, or thelike), a coloring dye (for example, an organic solvent-soluble azo dye,a water-soluble azo metal dye, or the like), an inorganic pigment (forexample, titanium oxide or the like), a chelating agent (for example,thiol or the like), a conductive pigment (for example, a metal powder ofzinc, aluminum, nickel, or the like, iron phosphide, antimony-doped tinoxide, or the like), a coupling agent (for example, a silane couplingagent, a titanium coupling agent, or the like), a melamine-cyanuric acidadduct; and the like.

The surface-treated steel sheet is produced by coating the surfaces of asteel sheet having a zinc-containing or aluminum-containing coating witha treatment solution containing the components for the composite oxidefilm, heat-drying the steel sheet, coating the steel sheet with acoating composition containing the specified organic polymeric resin (A)and the rust-proofing additive (B) (preferably as main components), andfurther containing the solid lubricant and the like according to demand,and then heat-drying the coated steel sheet.

The surfaces of the plated-steel sheet can be previously subjected toalkali degreasing and pre-treatment such as surface control treatmentfor further improving adhesion and corrosion resistance before thecoating with the treatment solution according to demand.

In order to treat the surface of the plated steel sheet having thezinc-containing coating or aluminum-containing coating with thetreatment solution to form the composite oxide film (first layer film),the treatment solution preferably contains the following components:

-   -   (α) silica;    -   (β) phosphoric acid and/or a phosphoric acid compound;    -   (γ) at least one selected from the group consisting of metal        ions of Mg, Mn, and Al, water-soluble ions containing at least        one of the metals, compounds containing at least one of the        metals, and complex compounds containing at least one of the        metals; and    -   (δ) a tetravalent vanadium compound.

The treatment solution (aqueous) further contains the additives (anorganic resin component, iron group metal ions, a corrosion inhibitor,and other additives) according to demand. After the treatment, theplated steel sheet is preferably dried by heating.

As a method for coating the steel sheet surfaces with the treatmentsolution for the first layer film, any one of a coating method, adipping method, and a spray method may be used. The coating method maybe performed with any coating means such as a roll coater (three-rollsystem or two-roll system, or the like), a squeeze coater, a die coater,or the like. After the coating treatment with a squeeze coater, thedipping treatment, or the spray treatment, control of the coatingamount, and uniformalization of appearance and thickness can beperformed by an air knife method or a roll squeeze method. Although thetemperature of the treatment solution is not particularly limited, thetemperature is properly room temperature to about 60° C. A temperatureof less than room temperature is uneconomical because a coolingapparatus or the like is required, while a temperature of over 60° C.causes difficulty in control of the treatment solution because thesolvent easily evaporates.

As described above, drying is performed by heating without water-washingafter coating with the treatment solution. The treatment solution usedin the present invention forms a slightly soluble salt by reaction withthe plated steel sheet used as the base, and thus water-washing may beperformed after the treatment. The coated treatment solution is dried byany desired heating method. For example, means such as a dryer, ahot-air furnace, a high-frequency induction heating furnace, an infraredfurnace, or the like may be used. From the viewpoint of corrosionresistance, the high-frequency induction heating furnace is preferred.The heat-drying is preferably performed at a reachable sheet temperaturein a range of 50° C. to 300° C., more preferably 80° C. to 200° C., andmost preferably 80° C. to 160° C. When the heat-drying temperature is50° C. or more, the sufficient corrosion resistance can be obtained.However, a heat-drying temperature of 300° C. or less is economical.

As described above, the composite oxide film is formed as the firstlayer film on a surface of the plated steel sheet having azinc-containing or aluminum-containing coating. Then, the coatingcomposition for forming the second layer film (organic film) is coatedon the first layer film. As the method for coating the coatingcomposition, any one of a coating method, a dipping method, and a spraymethod may be used. The coating method may be performed with any coatingmeans such as a roll coater (three-roll system or two-roll system, orthe like), a squeeze coater, a die coater, or the like. After thecoating treatment with a squeeze coater, the dipping treatment, or thespray treatment, control of the coating amount and uniformalization ofappearance and thickness can be performed by an air knife method or aroll squeeze method.

After coating with the coating composition, drying is performed byheating without water-washing. However, water-washing may be performedafter coating of the coating composition. Heat-drying may be performedwith means such as a dryer, a hot-air furnace, a high-frequencyinduction heating furnace, an infrared furnace, or the like. From theviewpoint of corrosion resistance, the high-frequency induction heatingfurnace is preferred. The drying by heating is preferably performed at areachable sheet temperature in a range of 50° C. to 350° C., and morepreferably 80° C. to 250° C. When the heat-drying temperature is 50° C.or more, the sufficient corrosion resistance can be obtained. However, aheat-drying temperature of 350° C. or less is economical.

The above-descried films are formed on one or both of the surfaces ofthe steel sheet. Therefore, the forms of the steel sheet of the presentinvention include the following:

-   -   (1) One side: plating film-composite oxide film-organic film,        the other side: plating film    -   (2) One side: plating film-composite oxide film-organic film,        the other side: plating film-known phosphate-treated film    -   (3) Both sides: plating film-composite oxide film-organic film    -   (4) One side: plating film-composite oxide film-organic film,        the other side: plating film-composite oxide film    -   (5) One side: plating film-composite oxide film-organic film,        the other aide: plating film-organic film

EXAMPLES

In order to form a first layer film, silica (α) shown in Table 1,phosphoric acid and/or phosphoric acid compound (β) shown in Table 2, aMn phosphate, Mg phosphate, or Al phosphate as a metal compound (γ)containing a metal component shown in Table 3, and a tetravalentvanadium compound (δ) shown in Table 4 were appropriately mixed withwater to prepare a treatment solution. In order to form a second layerfilm, the resin (A) shown in Table 5 and the rust-proofing additive (B)shown in Table 6 were appropriately mixed to prepare a coatingcomposition.

Each of the D-modified resin A′ and D-modified resin A″ shown in Table 5was synthesized by the method below.

[D-modified Resin A′]

In a four-necked flask, 1870 parts of EP828 (produced by Yuka ShellEpoxy Co. Ltd., epoxy equivalent 187), 912 parts of bisphenol A, 2 partsof tetraethylammonium bromide, and 300 parts of methyl isobutyl ketonewere charged, and the resultant mixture was heated to 140° C., followedby reaction for 4 hours. As a result, an epoxy resin having an epoxyequivalent 1391 and a solid content of 90% was obtained. To the epoxyresin, 1500 parts of ethylene glycol monobutyl ether was added, and thenthe resulting mixture was cooled to 100° C. Then, 96 parts of3,5-dimethylpyrozole (molecular weight 96) and 129 parts of dibutylamine(molecular weight 129) were added to the mixture, followed by reactionfor 6 hours until the epoxy groups disappeared. Then, 205 parts ofmethyl isobutyl ketone was added under cooling to obtainpyrazole-modified epoxy resin having a solid content of 60%. Thepyrazole-modified epoxy resin is referred to as “D-modified resin A′”.The resin (A′) corresponds to the product (X) of reaction between thefilm forming organic resin (A) and the active hydrogen-containingmaterial (D) containing 50 mol % of the hydrazine derivative (C) havingactive hydrogen.

[D-modified Resin A″]

In a four-necked flask, 4000 parts of EP1007 (produced by Yuka ShellEpoxy Co. Ltd., epoxy equivalent 2000) and 2239 parts of ethylene glycolmonobutyl ether were charged, and the resultant mixture was heated to120° C. to completely dissolve the epoxy resin over 1 hour. Theresultant solution was cooled to 100° C., and 168 parts of3-amino-1,2,4-triazole (molecular weight 84) was added to the solution,followed by reaction for 6 hours until the epoxy groups disappeared.Then, 540 parts of methyl isobutyl ketone was added to the reactionsolution under cooling to obtain triazole-modified epoxy resin having asolid content of 60%. The triazole-modified epoxy resin is referred toas “D-modified resin A″”. The resin (A″) corresponds to the product (X)of reaction between the film-forming organic resin (A) and the activehydrogen-containing material (D) containing 100 mol % of the hydrazinederivative (C) having active hydrogen.

As a raw material sheet to be treated, each of the plated steel sheetsshown in Table 7 was used. The surfaces of the plated steel sheets weresubjected to alkali degreasing and then washed with water and dried.Then, the treatment solution for forming the first layer film wascoated, and dried with a high-frequency induction heating furnace sothat the reachable sheet temperature was 140° C. Next, the coatingcomposition for forming the second layer film was coated, dried with ahigh-frequency induction heating furnace so that the reachable sheettemperature was 140° C., to form surface-treated steel sheets ofexamples of this invention and comparative examples. The thickness ofeach of the first layer film and the second layer film was controlled bycontrolling the residue of the film composition after heating, thetreatment time, or the like.

The types of the plated steel sheets and the compositions of the firstlayer film are shown in Tables 8-1, 8-2 and 8-3, and the compositions ofthe second layer film are shown in Tables 9-1, 9-2, and 9-3. Theevaluation results of qualities (coating appearance, corrosionresistance, and conductivity) of the surface-treated steel sheets areshown in Tables 10-1, 10-2, and 10-3.

The measurement and evaluation methods of each quality were as follows:

(1) Coating Appearance after Wetting Test

Each of samples was allowed to stand at 80° C. and a relative humidityof 98% for 1 day, and then the coating appearance was visually evaluatedon the basis of the following criteria:

-   -   A: Neither coloring nor discoloration (the same as before the        wetting test)    -   B: Slight coloring which could be recognized when observed        obliquely    -   B-: Obvious coloring and discoloration with an area ratio of        less than 5%    -   C: Obvious coloring and discoloration with an area ratio of 5%        to less than 20%    -   D: Obvious coloring and discoloration with an area ratio of 20%        or more        (2) Resistance to White Rust

Each sample was subjected to a salt-water spray test (JIS-Z-2371), andthe area ratio of white rust was evaluated after a predetermined time onthe basis of the following criteria:

-   -   A: Area ratio of white rust of less than 5%    -   B: Area ratio of white rust of 5% to less than 10%    -   B-: Area ratio of white rust of 10% to less than 25%    -   C: Area ratio of white rust of 25% to less than 50%    -   D: Area ratio of white rust of 50% to 100%        (3) Conductivity

The interlayer insulation resistance was measured according to JISC2550. Evaluation was performed on the basis of the following criteria:

-   -   A: less than 3 Ωcm²/sheet    -   B: 3 to 5 Ωcm²/sheet    -   C: over 5 Ωcm²/sheet

Tables 10-1, 10-2, and 10-3 indicate that the examples of this inventionare excellent in coating appearance after the wetting test, resistanceto white rust (corrosion resistance), and conductivity. On the otherhand, the comparative examples are inferior to the examples of thisinvention in any one of coating appearance after the wetting test,resistance to white rust (corrosion resistance), and conductivity.

As described above, the surface-treated steel sheets exhibit excellentcorrosion resistance even when coatings do not contain a pollutioncontrol substance such as hexavalent chromium, and also have excellentconductivity and coating appearance.

TABLE 1 No. (α) Silica 1 Snowtex OS 2 Snowtex O 3 AEROSIL 200 4 AEROSIL300

TABLE 2 (β) Phosphoric acid/ No. phosphoric acid compound 1Orthotriphosphoric acid 2 Pyrophosphoric acid

TABLE 3 (γ) Metal component No. in metal compound 1 Mg 2 Mn 3 Al

TABLE 4 (δ) Vanadium No. compound Valency 1 VOSO₄ 4 2 VCl₄ 4 3 V₂O₄ 4 4NH₄VO₃ 5 5 VCl₃ 3 6 VO 2

TABLE 5 No. Organic resin (A) 1 Epoxy resin 2 Urethane resin 3D-modified resin A′ 4 D-modified resin A″

TABLE 6 Rust-proofing additive (B) (e) Triazoles, thiols, (b) Ca ion-thiadiazoles, thiazoles, No. (a) Phosphate exchanged silica (c)Molybdate (d) Silicon oxide or thiurams 1 Zinc phosphate — — — — 2 — Caion- — — — exchanged silica 3 — — Al phosphate — — molybdate 4 — —Colloidal silica — 5 — — Tetraethylthiuram disulfide

TABLE 7 Coating weight* No. Plated steel sheet (g/m²) 1Electrogalvanized steel sheet 20 2 Hot-dip galvanized steel sheet 60 3Alloying hot-dip galvanized steel sheet 60 (Fe: 10 wt %) 4 Zn—Ni alloyplated steel sheet (Ni: 12 wt %) 20 5 Zn—Co alloy plated steel sheet(Co: 0.5 wt %) 20 6 Zn—Cr alloy plated steel sheet (Cr: 12 wt %) 20 7Hot-dip Zn—Al—Mg alloy plated steel sheet 90 (Al: 5 wt %, Mg: 0.5 wt %)8 Electrically Zn—SiO₂ dispersion-plated steel 20 sheet 9 Zn—Al—Mg alloyplated steel sheet 120 (Al: 6 wt %, Mg: 3 wt %) 10 Hot-dip Zn—Mg alloyplated steel sheet 150 (Mg: 0.5 wt %) *Coating weight on each side

TABLE 8-1 First layer film (β) Phosphoric acid/phosphoric (γ) (δ) (α)Silica acid compound Metal component Vanadium compound Coating weightPlated Coating weight Coating weight in terms of Coating weight steelType in terms of Type in terms of Type Mn, Al or Type in terms of VSection No. sheet *1 *2 SiO² (mg/m²) *3 P (mg/m²) *4 Mg (mg/m²) *5(mg/m²) Comp. Example 1 1 1 100 1 50 1 25 3 0 Example 2 1 1 100 1 50 125 3 10 Example 3 1 1 100 1 50 1 25 3 30 Example 4 1 1 100 1 50 1 25 350 Example 5 1 1 100 1 50 1 25 3 70 Example 6 1 1 100 1 50 1 25 1 10Example 7 1 1 100 1 50 1 25 2 10 Comp. Example 8 1 1 100 1 50 1 25 4 10Comp. Example 9 1 1 100 1 50 1 25 5 10 Comp. Example 10 1 1 100 1 50 125 6 10 Example 11 2 1 100 1 50 1 25 3 10 Example 12 3 1 100 1 50 1 25 310 Example 13 4 1 100 1 50 1 25 3 10 Example 14 5 1 100 1 50 1 25 3 10Example 15 6 1 100 1 50 1 25 3 10 Example 16 7 1 100 1 50 1 25 3 10Example 17 8 1 100 1 50 1 25 3 10 Example 18 9 1 100 1 50 1 25 3 10 *1:Plated steel sheet No. shown in Table 7 *2: Silica No. shown in Table 1*3: Phosphoric acid/phosphoric acid compound No. shown in Table 2 *4:Metal component No. shown in Table 3 *5: Vanadium compound No. shown inTable 4

TABLE 8-2 First layer film (β) Phosphoric acid/phosphoric (γ) (δ) (α)Silica acid compound Metal component Vanadium compound Coating weightPlated Coating weight Coating weight in terms of Coating weight steelType in terms of Type in terms of Type Mn, Al or Type in terms of VSection No. sheet *1 *2 SiO² (mg/m²) *3 P (mg/m²) *4 Mg (mg/m²) *5(mg/m²) Example 19 10 1 100 1 50 1 25 3 10 Comp. Example 20 1 1 0 1 50 125 3 10 Example 21 1 1 500 1 50 1 25 3 10 Example 22 1 1 2000 1 50 1 253 10 Comp. Example 23 1 1 2500 1 50 1 25 3 10 Example 24 1 2 100 1 50 125 3 10 Example 25 1 3 100 1 50 1 25 3 10 Example 26 1 4 100 1 50 1 25 310 Comp. Example 27 1 1 100 1 0 1 25 3 10 Example 28 1 1 100 1 250 1 253 10 Example 29 1 1 100 1 800 1 25 3 10 Comp. Example 30 1 1 100 1 11001 25 3 10 Example 31 1 1 100 2 50 1 25 3 10 Comp. Example 32 1 1 100 150 1 0 3 10 Example 33 1 1 100 1 50 1 250 3 10 Example 34 1 1 100 1 50 1600 3 10 Comp. Example 35 1 1 100 1 50 1 900 3 10 Example 36 1 1 100 150 2 25 3 10 *1: Plated steel sheet No. shown in Table 7 *2: Silica No.shown in Table 1 *3: Phosphoric acid/phosphoric acid compound No. shownin Table 2 *4: Metal component No. shown in Table 3 *5: Vanadiumcompound No. shown in Table 4

TABLE 8-3 First layer film (β) Phosphoric acid/phosphoric (γ) (δ) (α)Silica acid compound Metal component Vanadium compound Coating weightPlated Coating weight Coating weight in terms of Coating weight steelType in terms of Type in terms of Type Mn, Al or Type in terms of VSection No. sheet *1 *2 SiO² (mg/m²) *3 P (mg/m²) *4 Mg (mg/m²) *5(mg/m²) Example 37 1 1 100 1 50 3 25 3 10 Example 38 1 1 100 1 50 1 25 310 Example 39 1 1 100 1 50 1 25 3 10 Example 40 1 1 100 1 50 1 25 3 10Example 41 1 1 100 1 50 1 25 3 10 Example 42 1 1 100 1 50 1 25 3 10Example 43 1 1 100 1 50 1 25 3 10 Example 44 1 1 100 1 50 1 25 3 10Comp. Example 45 1 1 100 1 50 1 25 3 10 Example 46 1 1 100 1 50 1 25 310 Example 47 1 1 100 1 50 1 25 3 10 Comp. Example 48 1 1 100 1 50 1 253 10 Comp. Example 49 1 1 100 1 50 1 25 3 10 Example 50 1 1 100 1 50 125 3 10 Example 51 1 1 100 1 50 1 25 3 10 Example 52 1 1 100 1 50 1 25 310 Example 53 1 1 100 1 50 1 25 3 10 Comp. Example 54 1 1 100 1 50 1 253 10 *1: Plated steel sheet No. shown in Table 7 *2: Silica No. shown inTable 1 *3: Phosphoric acid/phosphoric acid compound No. shown in Table2 *4: Metal component No. shown in Table 3 *5: Vanadium compound No.shown in Table 4

TABLE 9-1 Second layer film Rust- Com- Organic proofing pounding Thick-resin additive (B) ratio (A)/(B) ness Section No. (A) *6 *7 *8 (μm)Comp. Example 1 3 2 100:30 1.0 Example 2 3 2 100:30 1.0 Example 3 3 2100:30 1.0 Example 4 3 2 100:30 1.0 Example 5 3 2 100:30 1.0 Example 6 32 100:30 1.0 Example 7 3 2 100:30 1.0 Comp. Example 8 3 2 100:30 1.0Comp. Example 9 3 2 100:30 1.0 Comp. Example 10 3 2 100:30 1.0 Example11 3 2 100:30 1.0 Example 12 3 2 100:30 1.0 Example 13 3 2 100:30 1.0Example 14 3 2 100:30 1.0 Example 15 3 2 100:30 1.0 Example 16 3 2100:30 1.0 Example 17 3 2 100:30 1.0 Example 18 3 2 100:30 1.0 *6:Organic resin No. shown in Table 5 *7: Rust-proofing additive No. shownin Table 6 *8: Weight ratio

TABLE 9-2 Second layer film Rust- Com- Organic proofing pounding Thick-resin additive (B) ratio (A)/(B) ness Section No. (A) *6 *7 *8 (μm)Example 19 3 2 100:30 1.0 Comp. Example 20 3 2 100:30 1.0 Example 21 3 2100:30 1.0 Example 22 3 2 100:30 1.0 Comp. Example 23 3 2 100:30 1.0Example 24 3 2 100:30 1.0 Example 25 3 2 100:30 1.0 Example 26 3 2100:30 1.0 Comp. Example 27 3 2 100:30 1.0 Example 28 3 2 100:30 1.0Example 29 3 2 100:30 1.0 Comp. Example 30 3 2 100:30 1.0 Example 31 3 2100:30 1.0 Comp. Example 32 3 2 100:30 1.0 Example 33 3 2 100:30 1.0Example 34 3 2 100:30 1.0 Comp. Example 35 3 2 100:30 1.0 Example 36 3 2100:30 1.0 *6: Organic resin No. shown in Table 5 *7: Rust-proofingadditive No. shown in Table 6 *8: Weight ratio

TABLE 9-3 Second layer film Rust- Com- Organic proofing pounding Thick-resin additive (B) ratio (A)/(B) ness Section No. (A) *6 *7 *8 (μm)Example 37 3 2 100:30 1.0 Example 38 4 2 100:30 1.0 Example 39 1 2100:30 1.0 Example 40 2 2 100:30 1.0 Example 41 3 1 100:30 1.0 Example42 3 3 100:30 1.0 Example 43 3 4 100:30 1.0 Example 44 3 5 100:30 1.0Comp. Example 45 3 — 100:0  1.0 Example 46 3 2 100:70 1.0 Example 47 3 2 100:100 1.0 Comp. Example 48 3 2  100:150 1.0 Comp. Example 49 — — — —Example 50 3 2 100:30 0.1 Example 51 3 2 100:30 0.5 Example 52 3 2100:30 3.0 Example 53 3 2 100:30 5.0 Comp. Example 54 3 2 100:30 10.0 *6: Organic resin No. shown in Table 5 *7: Rust-proofing additive No.shown in Table 6 *8: Weight ratio

TABLE 10-1 Performance Resistance Resistance Film Resistance to to whiteto white Con- appear- white rust rust after rust after duc- Section No.ance after 140 hr 200 hr 260 hr tivity Comp. 1 A C D D A Example Example2 A A A A A Example 3 B A A A A Example 4 B- A A A A Example 5 C A A A AExample 6 B A A B A Example 7 B A A B A Comp. 8 B B B- C A Example Comp.9 B B- C C A Example Comp. 10 B B- C C A Example Example 11 A A A A AExample 12 A A A A A Example 13 A A A A A Example 14 A A A A A Example15 A A A A A Example 16 A A A A A Example 17 A A A A A Example 18 A A AA A

TABLE 10-2 Performance Resistance Resistance Film Resistance to to whiteto white Con- appear- white rust rust after rust after duc- Section No.ance after 140 hr 200 hr 260 hr tivity Example 19 A A A A A Comp. 20 A CD D A Example Example 21 B A A A A Example 22 B- A A A A Comp. 23 C A AA A Example Example 24 A A A A A Example 25 A A A A A Example 26 A A A AA Comp. 27 A D D D A Example Example 28 A A A B A Example 29 A A B B- AComp. 30 A B B- C A Example Example 31 A A A A A Comp. 32 A C D D AExample Example 33 B A A B A Example 34 B- A B B- A Comp. 35 C B B- C AExample Example 36 A A A A A

TABLE 10-3 Performance Resistance Resistance Film Resistance to to whiteto white Con- appear- white rust rust after rust after duc- Section No.ance after 140 hr 200 hr 260 hr tivity Example 37 A A A A A Example 38 AA A A A Example 39 A A A B A Example 40 A A A B A Example 41 A A A A AExample 42 A A A A A Example 43 A A A A A Example 44 A A A A A Comp. 45A C D D A Example Example 46 A A A B A Example 47 A A B B- A Comp. 48 AB B- C A Example Comp. 49 A D D D A Example Example 50 A B B- B- AExample 51 A B B B- A Example 52 A A A A A Example 53 A A A A A Comp. 54A A A A B Example

INDUSTRIAL APPLICABILITY

The surface-treated steel sheet has excellent corrosion resistance,conductivity, and coating appearance without containing a pollutioncontrol substance such as hexavalent chromium or the like. Therefore,the surface-treated steel sheet can be applied to a wide range ofapplications such as automobiles, home electric appliances, buildingmaterials, and the like without adversely affecting workers, users, orenvironments.

1. A surface-treated steel sheet comprising: a steel sheet; a platinglayer provided on at least one of the surfaces of the steel sheet, theplating layer containing at least one metal selected from the groupconsisting of zinc and aluminum; a first layer film provided on thesurface of the plating layer and containing (α) 1 to 2000 mg/m² ofsilica in terms of SiO₂, (β) a total of 1 to 1000 mg/m² of phosphoricacid groups in terms of P, (γ) a total of 0.5 to 800 mg/m² of at leastone metal selected from the group consisting of Mg, Mn, and Al in termsof a metal element, and (δ) 0.1 to 50 mg/m² of a tetravalent vanadiumcompound in terms of V; and a second layer film formed to a thickness of0.1 to 5 μm on the first layer film and containing a polymeric resin (A)having at least one type of functional group selected from the groupconsisting of OH and COOH groups, and at least one rust-proofingadditive (B) selected from the group consisting of the followingcompounds (a) to (e): (a) a phosphate; (b) Ca ion-exchanged silica; (c)a molybdate; (d) silicon oxide; and (e) at least one organic compoundselected from the group consisting of triazoles, thiols, thiadiazoles,thiazoles, and thiurams.
 2. The surface-treated steel sheet according toclaim 1, wherein the resin (A) is a product (X) of reaction of afilm-forming organic resin with an active hydrogen-containing substance(D) partially or entirely comprising a hydrazine derivative (C) havingactive hydrogen.
 3. A surface-treated steel sheet having excellentcorrosion resistance, conductivity, and coating appearance, the steelsheet comprising: a steel sheet having a zinc-based or aluminum-basedcoating; a composite oxide film formed as a first layer film on asurface of the steel sheet and containing (α) silica, (β) phosphoricacid and/or a phosphoric acid compound, (γ) at least one metal selectedfrom the group consisting of Mg, Mn, and Al wherein said at least onemetal is elemental, a compound, and/or a complex compound, and (δ) atetravalent vanadium (IV) compound, the coating weights of thesecomponents being as follows: (α) silica: 1 to 2000 mg/m² in terms ofSiO₂; (β) phosphoric acid and/or a phosphoric acid compound: a total of1 to 1000 mg/m² in terms of P; (γ) at least one metal selected from thegroup consisting of Mg, Mn, and Al: a total of 0.5 to 800 mg/m² in termsof Mg, Mn, or Al; and (δ) a tetravalent vanadium compound: 0.1 to 50mg/m² in terms of V; and an organic film formed as a second layer filmhaving a thickness of 0.1 to 5 μm on the first layer film and containingan organic polymeric resin (A) having an OH group and/or a COOH group,and at least one rust-proofing additive (B) selected from the groupconsisting of the compounds (a) to (e) below in a total of 1 to 100parts by mass (solid content) relative to 100 parts by mass (solidcontent) of the resin (A): (a) a phosphate; (b) Ca ion-exchanged silica;(c) a molybdate; (d) silicon oxide; and (e) at least one organiccompound selected from the group consisting of triazoles, thiols,thiadiazoles, thiazoles, and thiurams.